October Season: Close the Door
Three boxes, three doors left open on the way out — a passwordless-root sudoers backdoor, a SUID-root shell in the weeds, and an SSH config wide open with a stranger's key in it. Find each foothold, close it without breaking the legitimate access around it, and recover what they left behind. Sandboxes you fully control. Defensive hardening only.
Archived season — playable for practice, no leaderboard points. Official write-ups are open.
The Rule They Left Behind
security · sudo · sudoers
SUID in the Weeds
security · suid · privilege-escalation
Close the Door
security · ssh · hardening
Close the Door
400 pts · decays to 180 · +75 first bloodThe box was left wide open and someone made sure they could return: sshd permits direct root login and password auth, and /root/.ssh/authorized_keys carries a rogue key beside the legitimate admin key. Harden the config, purge the intruder's key without locking out the real admin, and recover the note they left in root's .ssh directory. Full root on an isolated box; grading reads the config and key files directly.
The live sandbox for this challenge isn't available yet — the brief is open.
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Submit flag
Complete every objective in the lab and use Verify & grade, then submit the flag from that same box here.
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Archived — solves are for practice, not the leaderboard.
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